Abrasive blast cleaning system

ABSTRACT

An abrasive blast cleaning system includes blast means for granulating and scouring the sand removed from a no-bake mold whereby the sand is reconditioned for reuse in a subsequent nobake molding operation.

United States Patent [191 Carpenter et a1.

[451 Aug. 13, 1974 ABRASIVE BLAST CLEANING SYSTEM Inventors: James H. Carpenter, Hagerstown,

Md; Joseph E. Bowling, Jr., Waynesboro, Pa.

Assignee: The Carborundum Company,

Niagara Falls, NY.

Filed: Nov. 15, 1972 Appl. No.: 306,769

Related US. Application Data Division of Ser. No. 108,417, Jan. 21, 1971, Pat. No. 3,716,947.

[56] References Cited UNITED STATES PATENTS 554,473 2/1896 Beeg 51/9 2,225,482 12/1940 Mulvany 51/9 2,478,461 8/1949 Connolly 241/D1G. 10

2,707,314 5/1955 Horth 241/D1G. 10

3,097,451 7/1963 Freeman 51/319 X 3,626,641 12/1071 Powell 51/9 X Primary ExaminerD0na1d G. Kelly Attorney, Agent, or FirmDavid E. Dougherty; William H. Holt [5 7] ABSTRACT An abrasive blast cleaning system includes blast means for granulating and scouring the sand removed from a no-bake mold whereby the sand is reconditioned for reuse in a subsequent no-bake molding operation.

9 Claims, 18 Drawing Figures aaasgozs PAIENIEU Anal 3 m4 SHEET 3. BF 7 ma ma PATENTED AUG 1 31974 SHEET 0F 7 AQQ Fl L PAIENTEDAUBI 14 3,829,029

SHEET 5 OF 7 PATENTEUAUBI 3W 3,829,029

SHEEI 5 [IF 7 ABRASIVE BLAST CLEANING SYSTEM This is a division, of copending application Ser. No. 108,417, filed Jan. 21, 1971 now US. Pat. No. 3,716,947.

BACKGROUND OF INVENTION A recent development in the casting industry is the use of chemical bonded molds. Essentially this practice utilizes quality sand, a chemical binder and a catalyst which are mixed together and hardened into a solid cake at ambient temperatures. Accordingly, baking is not required for such molds and the practice is, therefore, known in the art as no-bake" molding. Generally the base binder used in no-bake molding is either an acid base such as a chemical binder with phosphoric acid as the activator or is an oil base. In practice the nobake mold pattern is disposed in a topless frame on, for example a support table with the no-bake ingredients being added to form a cavity corresponding to one portion of the casting and rigidifying rods added thereto. The mold is then inverted and the complementary portion of the no-bake mold is formed thereon so that the resultant composite cavity corresponds to the casting. Suitable gating is of course also provided. This practice is generally similar to standard foundry techniques but thus differs in'at least one major respect, namely, the no-bake molding equipment does not require a heavy flask in which to house the sane when the molten metal is subsequently applied to the cavity. Even the topless frame used initially in the process is not needed during the casting forming step.

The no-bake molding process potentially represents a significant advancement in the foundry art since it offers a number of distinct advantages. For example the molds are easier to make without requiring a skilled molder. There is a cleaner environment with less dust and spillage than with green sand molding. The nobake technique is quicker since jolt mechanisms are not required. Simple form boxes or topless frames are merely necessary to shape the mold rather than the conventional heavy flasks. The molds can be handled without breaking apart by providing a grid plate or strapping and thereby the mold with its casting can be moved to a shaker or cleaning process without breaking apart. It has been suggested that the mold shell or sand can be removed by blasting and in such case the mold shell and core can be handled to the interior of a blast machine where the sand and dust can be contained and shakeout noise eliminated. Moreover, the casting finish is thereby improved and casting tolerances can be tightened with the castings matching the pattern. The castings can go directly to numerically controlled machines, thereby obviating the need for rough cuts on manual machines.

Despite, the numerous advantages such as indicated above which are possible with no-bake molding, there are a number of serious disadvantages which might cause this process to be unacceptable in the foundry art. These disadvantages include the increased costs for quality grade sand which might cost three or four times more than the cost of green sands. Since quality sand is used this sand must be reclaimed for reuse to make the entire process economically feasible.

- Although attempts are being made at reclaiming and reusing the sand, experts cannot agree on the percentage of reclaiming possible with a system nor the qualities needed or obtained by a system. The publication, Foundry, Sept. 1970, pages 83-90, for example, described one such attempt at sandreclamation. The reclaimed sands with the present systems, however, are not uniform in qualities. In this respect the build-up of fines and/or organics seriously affects the molds using reclaimed sands. Moreover, proposed reclaiming systems require shakers, crushers or Muller type units which are noisy and dusty and also require rather large floor space and head room with high maintenance and capital costs.

SUMMARY OF INVENTION An object of this invention is to provide an abrasive blasting system which granulates and scours sand obtained from a no-bake molding operation.

A further object of this invention is to provide such a system which in a broader form may utilize the concepts herein for functioning as a granulating means, per,

A still further object of this invention is to provide various alternatives for effectively granulating and/or scouring sand or other lumpy granular material.

In accordance with this invention an abrasive blast cleaningsystem includes blast means for granulating and scouring the sand removed from a no-bake mold whereby the sand is reconditioned for reuse in a subsequent no-bake molding operation.

The sand itself may be initially obtained by blasting abrasive particles against a no-bake mold wherein the sand in lumpy and granular form is conveyed along with spent abrasive, rods, fines and other contaminants toward the granulating and scouring station. The finer materials may undergo a separation operation to remove the finer granular sand from the remainder of the mixture and this granular sand may be dropped adjacent'an impact plate where the grains are struck by abrasive particles to reduce any build-up of binder on the sand by removing binder from the grains. The same blast means which reduces a binder build-up is also used to break the lumps into fine granular form and simultaneously to clean the rods in the mixture. Thus the rods also are put into condition for reuse simultaneously with the granulating and scouring of the sand.

THE DRAWINGS FIG. 1 is a side elevation view schematically showing one embodiment of this invention; FIG. 2 is a plan view of the embodiment of the invention shown in FIG. 1;

FIG. 3 is a cross-sectional view taken through FIG. 2 along the line 3-3;

FIG. 3A is a view similar to FIG. 3 showing an alternative conveyor structure;

FIG. 4 is an elevation view of a portion of a modified blast chamber;

FIGS. 5 and 6 are views similar to FIG. 3 on an enlarged scale of alternative arrangements of this invention;

FIGS. 7-8 are side and end elevation views of yet another embodiment of this invention;

FIGS. 9-10 are cross-sectional views in elevation schematically illustrating another embodiment of this invention;

FIG. 11 is a plan view in section illustrating a portion of the embodiment shown in FIG. 10;

FIG. 12 is a plan view in section similar to FIG. 11 showing still another embodiment of this invention;

FIG. 13 is a cross-sectional view in elevation of yet another embodiment of this invention;

FIG. 14 is a cross-sectional view taken through FIG. 13 along the line 1414;

FIG. 15 is a cross-sectional view in elevation of still yet another embodiment of this invention;

FIG. 16 is a plan view in section of a portion of the embodiment shown in FIG. 15; and

FIG. 17 is an elevation view partly in section of yet another embodiment of this invention.

DETAILED DESCRIPTION FIG. 1 shows the abrasive cleaning system 10 in accordance with this invention. As indicated therein a nobake mold 12 is held in an open frame 14 and conveyed on monorail 16 into blast chamber 18. As is conventional with such no-bake molds rigidifying rods 20 as well as a casting 22 are embedded in the sand 24. Means 26 are provided to suspend the casting when the sand is later removed.

Blast chamber 18 is provided with a plurality of centrifugal throwing wheels 28 which project abrasive particles against the mold to remove the sand and rods therefrom and thereby clean the then exposed casting in one operation. When the sand is removed from the mold it has been found that about percent of the sand is in lump form while the remaining 75 percent is in small granular form. The falling sand, rods, spent abrasive, fines and other contaminants fall through the bottom 30 of chamber 18 and are received on oscillating conveyor 32. To facilitate the discharge of this mixture of sand, abrasive, etc., from chamber 18 the floor of the chamber is made with maximal open area. Ideally chamber 18 would be completely floorless. It is generally desired, however, to have some structural members at the bottom of chamber 18 to permit workmen to enter for various purposes. Thus as shown in FIG. 1 spaced I-beams 34 are provided so that the mixture 36 can be received on the oscillating conveyor 32 by falling through the large open area between I-beams 34. FIG. 4 shows an alternative arrangement wherein the floor is made of louvered members 38 thereby advantageously providing a support area which can be walked on but facilitating the discharge of the mixture through the floor.

The entire mixture 36 is conveyed on oscillating conveyor 32 until the mixture reaches a portion of the conveyor which includes a screen 40 of appropriate mesh size to permit the fine grain abrasives, fines. and other contaminants to fall into hopper 42 and thence to screw conveyor 44 where it is received by elevator 46 for separation as later described. The remaining portion of mixture 36 which includes lumps, rods, and any other elements which may be carried with the mixture is conveyed to the end of oscillator 32 and drops onto generally perpendicular oscillating conveyor 48 until it reaches the second blast station 50 (FIG. 2).

In the meantime the mixture in elevator 46 is discharged into screw conveyor 52 and into any suitable number of separators 54. Advantageously, separators 54 are of the air wash type such as described and illustrated in US. Pat. 3,368,677 the details of which are incorporated herein by reference thereto. In general the air wash separator 54 subjects the falling mixture to an air curtain supplied for example at inlet 56.- A numher of skimmer plates 58 are provided in the separating chamber 60 to facilitate a separation of the mixture into individual streams in accordance with their weight. In this respect the abrasive particles are heavier than the sand which in turn is heavier than the fines. Thus the abrasive particles fall generally directly downward into discharge conduit 62 while the fine grained sand is slightly diverted and received in discharge conduit 64. Other discharge conduits (not shown) are provided for the fines and other contaminants.

It has been found that the sand in the mixture fed to separators 54 is not always of the desired size of fineness but frequently is in smaller lumps which may be termed pea size. Generally such pea sized lumps are about three-sixteenths to one-fourth inch in diameter. Since this pea size sand is heavier than the fine grain size, the pea size sand will also go into conduit 62 with the abrasive particles which are large size metal shot. Accordingly, it is necessary that this sand be separated from the abrasive particles if the sand recovered is to be maximized not only for reuse of the sand but also for reuse of the abrasive particles. Accordingly, the mixture of pea size sand and abrasive particles undergoes a second separation process. This second separation process includes feeding the mixture of abrasive particles and pea size sand through pairs of rollers 66 which may be made of wear resistant polyurethane. The closely positioned rotating rollers crush the pea-size sand into its fine granular form while of course permitting the abrasive particles to retain their normal size. This mixture of crushed sand and abrasive particles is then fed into separators 68 which are of the air wash type similar to separators 54 except that only one skimmer plate 70 is necessary since the mixture will be divided into only two streams. It is to be understood, however, that a separator using a plurality of skimmer plates may also be used. The substantially pure abrasive particles are received in spout 72 for reuse by blast wheels 28 by conveyance through pipes 74. The fine grain sand is received in hopper 76 where it mixes with the fine grain flowing from conduits 64 and is conveyed through conduit 78 to the blast station 50.

A particular advantage of this invention is the inclusion of blast station 50 which in effect both granulates and scours the sand as is essential for the sand reclamation that would be necessary to render the no-bake molding process economically feasible. In this respect as previously noted about 25 percent of the sand in mixture 36 is in lump size which could for example vary from 1 inch to 10 inches in general diameter. In accordance with this invention the lumps and core rods are handled through the blast station without damage to any mechanism. Advantageously, the same blast station 50 which granulates and reconditions the sand also simultaneously cleans the rods so that the rods are free of any residual material and thus are in condition for reuse. The arrangement provides these advantages with minimum floor space requirements and is both noise free and dust free within acceptable limits. As previously noted in order to reclaim the sand in a condition for reuse it is necessary not only to granulate the sand back to its normal size but also to scour the sand. By scouring the sand is meant removing the organics or binder material used in the no-bake process. Although it is not completely agreed as to how much binder material may remain on the sand without hampering the reuseability of the sand, it is agreed that a build-up of binder material should be prevented.

The above advantages are achieved at blasting station 50 by the inclusion of a conventional centrifugal throwing wheel 80 which uses generally large size metal shot projected at a high flow rate at for example 1,200 to 1,700 rpm or lower. The metal shot strikes the lumps to granulate them while also knocking the organics off the grains of sand. Advantageously, the sand which has been separated by the separators 54 and 68 is also passed into the blast stream from wheel 80 so that the organic binder is removed from this sand. As shown for example in FIG. 3 the falling sand from conduit 78 drops between the blast stream 82 and a strike plate 84. In this manner the abrasive particles from a portion of stream 82 hit the falling sand and causes the sand grains to strike each other and to ricochet against the strike plate 84. The resulting impacts effectively remove the organic binder. In the meantime the remaining portion of blast stream 82 granulates and scours the lumps 86 and cleans the rods 20 which are moving on oscillating conveyor 48. A portion of oscillating conveyor 48 is provided with a screen 88 of appropriate mesh size to permit the granulated sand and abrasive particles to fall into hopper 89 to screw conveyor 90. The larger rods, however, continue to flow on oscillator 48 and are ultimately discharged and collected in any suitable receptacle (not shown). Thus the rods are received from blast station 50 in a cleaned condition for reuse.

From screw conveyor 90 the mixture of granulated reconditioned sand and abrasive particles are fed to elevator 92 and then to separator 94 whichalso is of the air wash type previously described including air curtain inlet 96 and skimmer plate 100 in separation chamber 98. The mixture is thereby divided into one stream of abrasive particles which is received in spout 102 and conveyed back to abrasive blast wheel 80 while the stream of reconditioned sand is received in spout 104 and discharged from outlet 107 and into any suitable receptacle (not shown)'for reuse.

Prior to discharge from outlet 106 the sand may pass through magnetic drum separator 107 to remove the small quantity of metal abrasive that may be mixed in with the otherwise substantially pure sand.

FIG. 5 shows an alternative arrangement similar to FIG. 3 wherein the mixture of lumps and rods, etc., is fed from conveyor 108 to oscillating conveyor 110 in a manner similar to the arrangement of FIG. 3. With this arrangement, however, blast wheel 112 uses as its blast particles not only metal shot supplied from conduit 114 but also the fine grained sand which is fed by conduit 116 as would be supplied for example from conduit 78. In this manner the line grain sand not only functions to break the lumps 118 but also the impact from the sand helps remove the binder therefrom. Such an arrangement would also permit a simplier separation system since it would not be as critical .to completely separate the fine grain sand from the abrasive particles in the mixture received from blast chamber 18.

Although FIG. 3 and various other Figures illustrate the conveying means for the lumpy material to be an oscillating conveyor other types of conveying means are also possible. Thus, for example, as shown in FIG. 3A the lumpy material 86 is conveyed on a belt 85 which is made of mesh form so as to permit the passage of abrasive particles and crushed lumpy material to pass therethrough onto incline 87 and thence into hopper 89 to screw conveyor 90. The conveying means need not have a flat surface such as illustrated in FIGS. 3 and 3A but may take any other suitable form such as for example being in the form of a drum conveyor in accordance with the particular results desired.

As previously indicated many suitable abrasive blast means may be used in accordance with this invention. One particularly effective blast means is the centrifugal throwing wheel shown and described in U.S. Pat. 3,348,339 which includes flared and tilted vanes. Additionally, it is also possible to use multiple throwing wheels at each blast station. Metal shot may advantageously be used as the abrasive particles.

FIG. 6 shows another alternative arrangement which maximizes the lump breaking ability of blast wheel 120. As indicated therein the oscillating conveyor 122 is of a particular design in that its upper surface includes steps thereby providing shoulders 124, 126. This arrangement is advantageous since the affect of the left hand portion of blast stream 128 is to drive the lumps back toward the left against the direction of flow imparted by oscillator 122. Shoulder 124, for example, however, acts as a stop to prevent this backward flow and to hold a lump 130 until it is effectively granulated so that it may fall through the mesh screen 132.

As shown, for example, in FIG. 1 the various oscillating conveyors used in the lump breaking stations are trough shaped and are of such a dimension as to confine the moving stream of lumpy sand into an area which has a width no greater than the width of the particularly arranged centrifugal throwing wheel blast stream so that the centrifugal throwing wheel can thoroughly function as a lump breaking means.

FIGS. 7-8 show a simplified form of this invention similar to the arrangement shown in FIG. 1. With the arrangement of FIGS. 7-8 when the fine granular sand removed from the no-bake mold in blast chamber 18 does not have a substantial binder build up, it is then possible to convey this fine sand into elevator 134 and thence to separating system 136 without subjecting the fine sand to'a scouring operation. In the meantime, however, the lumps from blast chamber 18 would be crushed at blast station 138 and the crushed lumps would then be conveyed to the same elevator 134 and separating system 136. In this manner, the arrangement of FIGS. 7-8 eliminates the need for a pair of elevators and separating systems such as shown in FIG. 1.

FIG. 9 illustrates another aspect of this invention which maximizes the scouring efficiency thereof. In this respect mixture 140 which includes lumps 142 is fed into hopper 144 from any suitable source such as a blast chamber which cleans a casting from a no-bake mold as previously described, or from any other source. The sand may, for example, be supplied from a batch barrel or may be continuously fed. As previously described, the mixture is fed into blasting station 146 whereby blast wheel 148 breaks the lumps and also subjects the sand in the mixture to a scouring treatment. The embodiment of FIG. 9 differs from previous embodiments in that means are provided to subject the granular sand to a further scouring operation. In this respect the bottom of blasting station 146 includes a collecting hopper 150 having an outlet which feeds the granular sand and abrasives into blast wheel 152. Blast wheel 152 is designed to project the thusly fed sand and blast wheel 152 would operate at a reduced speed such as 1,200 rpm rather than the conventional speed of 2,250 rpm.

FIGS. -11 show an arrangement similar to FIG. 9 in the inclusion of a further scouring abrasive blast station 156. In this arrangement, however, the mixture of sand and abrasive particles is discharged onto a flow distribution cone 158 so as to fall between impact plate 154 and blast wheel 160. Blast wheel 160 which has 360 blast coverage is supplied with abrasive particles through conduit 162 from separator 164 so that the falling stream distributed by cone 158 is struck by the blast particles centrifugal throwing wheel 160, and caused to ricochet against impact plate 154.

The utilization of flow distribution cone 158 in FIGS. 10-11 is highly beneficial for greater volume production. FIG. 12 illustrates an alternative shape for the flow distribution means. In this respect instead of a cone the flow distribution means is in the shape of a pair of inverted plates 159 which are inclined toward each other and meet at their apex to form an inverted V above blast wheel 161. Since the flow distribution plates 159 will merely have two streams flowing therefrom, blast wheel 161 includes an impeller case having two slots, so that the blast wheel will thereby project a pair of diametrically opposed blast streams.

FIGS. 13-14 show an advantageous arrangement for scouring the sand such as recieved from the previously described lump breaking station and discharged through spout 166. The discharged particles are fed into centrifugal throwing wheel 168 at blast station 170. In line with the vanes 172 of throwing wheel 168 is an impact or ricochet plate 174 inclined toward the blast wheel. The lower end of plate 174 is joined to a further impact plate 176 in such a manner that the particles are thrown off vanes 172 against plate 174 and ricochet off plate 174 downwardly against plate 176 and back toward the center of the blast station. In this manner there is a maximization of the turbulence created in the sand particles to thereby effectively scour these particles. If desired, an additional ricochet plate 178 may be provided to further increase the turbulence. Advantageously, the drive 180 for blast wheel 168 is enclosed in a shielded housing 182 which incorporates suitable power line conduit 184 and vent line 186.

FIGS. -16 show still another manner of obtaining a high degree of turbulence. As indicated therein the particles are discharged through spout 188 into centrifugal throwing wheel 190. The drive 189 for wheel 190 is housed in casing 191 with a suitable vent line 193 being provided. In this embodiment, however, the impact plates are a plurality of plates or vanes 192 projecting from the interior wall 194 of blast chamber 196.

FIG. 17 illustrates yet another ramification of this invention wherein a plurality of blast wheels 198, 200, 202 are stacked atop each other in such a manner that, for example, the particles projected from blast wheel 198 are fed through spout 204 into subsequent blast wheel 200 and then fed through spout 206 into blast wheel 202. Any number of vertically arranged blast wheels may be provided in accordance with the desired degree of scouring. The stacked arrangements may also include suitable vent line 208 and other features with respect to the individual wheels previously described.

It is to be understood that although the concepts of this invention have been described with particular reference to sand reclamation for the no-bake mold system, the concepts may be equally applied to other arrangements. Thus, for example the utilization of a blast wheel or, in fact, of any suitable blast particles projecting means (such as nozzles) in the manner described may be incorporated as a lump breaker, per se, whenever it is desired to granulate material.

This application incorporates by reference thereto, the subject matter disclosed in copending applications Ser. No. 85,645, filed Oct. 30, I970 in the name of Russell L. Rowe and now US. Pat. No. 3,690,066, and Ser. No. 89,181, filed Nov. 13, 1970 in the name of Joseph E. Bowling, Jr. and now US. Pat. No. 3,694,964, both of which are owned by the assignee of the present invention.

What is claimed is:

1. A method of abrasive blast treatment for producing granular material from lumpy material created from a mold used to make castings, said method comprising the steps of removing a casting from a mold and creating a mixture from said mold including granular material and lumpy material, projecting blast particles against at least said lumpy material for breaking up the same into granular material, and separating said blast particles from said granular material.

2. A method as defined in claim 1 including the step of collecting said blast particles following said separating step, and reusing the collected blast particles by again projecting them against said lumpy material.

3. A method as defined in claim 1 wherein said mold is a no-bake mold comprised of fine grained sand, binder material, rods, and contains a casting within said mold, and wherein the steps of removing a casing from a mold and creating a mixture from said mold include the steps of: projecting blast particles against said mold for breaking said mold into said mixture of granular material and lumpy material, and freeing said granular and lumpy material from said casting for cleaning said casting.

4. A method as defined in claim 3 wherein said step of projecting blast particles against said mold is performed at a first location and said step of projecting blast particles against at least said lumpy material is performed at a second location, said method further including the step of conveying at least said lumpy material and said rods from said first location to said second location, and cleaning said rods simultaneously while breaking up said lumpy material into fine grain sand.

5. A method as defined in claim 4 including the additional step of projecting said fine grain sand against an impact plate for scouring binder material therefrom.

6. A method as defined in claim 5 including the additional step of including blast particles with said fine grain sand during said step of projecting.

7. A method as defined in claim 1 wherein the step of separating said blast particles from said granular material includes the step of creating a free-falling stream of said blast particles and granular materials, passing a current of air through said free-falling stream for creating a first stream of blast particles and pea size granular granular material.

9. A method as defined in claim 1 including the step of creating a falling stream of said granular material and said blast particles prior to said separating step, and projecting additional blast particles against said falling stream for scouring said granular material. 

1. A method of abrasive blast treatment for producing granular material from lumpy material created from a mold used to make castings, said method comprising the steps of removing a casting from a mold and creating a mixture from said mold including granular material and lumpy material, projecting blast particles against at least said lumpy material for breaking up the same into granular material, and separating said blast particles from said granular material.
 2. A method as defined in claim 1 including the step of collecting said blast particles following said separating step, and reusing the collected blast particles by again projecting them against said lumpy material.
 3. A method as defined in claim 1 wherein said mold is a no-bake mold comprised of fine grained sand, binder material, rods, and contains a casting within said mold, and wherein the steps of removing a casint from a mold and creating a mixture from said mold include the steps of: projecting blast particles against said mold for breaking said mold into said mixture of granular material and lumpy material, and freeing said granular and lumpy material from said casting for cleaning said casting.
 4. A method as defined in claim 3 wherein said step of projecting blast particles against said mold is performed at a first location and said step of projecting blast particles against at least said lumpy material is performed at a second location, said method further including the step of conveying at least said lumpy material and said rods from said first location to said second location, and cleaning said rods simultaneously while breaking up said lumpy material into fine grain sand.
 5. A method as defined in claim 4 including the additional step of projecting said fine grain sand against an impact plate for scouring binder material therefrom.
 6. A metHod as defined in claim 5 including the additional step of including blast particles with said fine grain sand during said step of projecting.
 7. A method as defined in claim 1 wherein the step of separating said blast particles from said granular material includes the step of creating a free-falling stream of said blast particles and granular materials, passing a current of air through said free-falling stream for creating a first stream of blast particles and pea size granular material and a second stream of fine grain granular material, breaking up said pea size granular material into additional fine grain granular material, and then separating said additional fine grain granular material from said blast particles.
 8. A method as defined in claim 7 including the addition step of projecting said fine grain granular material against an impact plate for scouring said fine grain granular material.
 9. A method as defined in claim 1 including the step of creating a falling stream of said granular material and said blast particles prior to said separating step, and projecting additional blast particles against said falling stream for scouring said granular material. 